The importance of efficiently and safely administering pharmaceutical substances such as diagnostic agents and drugs has long been recognized. Although an important consideration for all pharmaceutical substances, obtaining adequate bioavailability of large molecules such as proteins that have arisen out of the biotechnology industry has recently highlighted this need to obtain efficient and reproducible absorption (Cleland et al., Curr. Opin. Biotechnol. 12: 212-219, 2001). The use of conventional needles has long provided one approach for delivering pharmaceutical substances to humans and animals by administration through the skin. Considerable effort has been made to achieve reproducible and efficacious delivery through the skin while improving the ease of injection and reducing patient apprehension and/or pain associated with conventional needles. Furthermore, certain delivery systems eliminate needles entirely, and rely upon chemical mediators or external driving forces such as iontophoretic currents or electroporation or thermalporation or sonophoresis to breach the stratum corneum, the outermost layer of the skin, and deliver substances through the surface of the skin. However, such delivery systems do not reproducibly breach the skin barriers or deliver the pharmaceutical substance to a given depth below the surface of the skin and consequently, clinical results can be variable. Thus, mechanical breach of the stratum corneum, such as with needles, is believed to provide the most reproducible method of administration of substances through the surface of the skin, and to provide control and reliability in placement of administered substances.
Approaches for delivering substances beneath the surface of the skin have almost exclusively involved transdermal administration, i.e. delivery of substances through the skin to a site beneath the skin. Transdermal delivery includes subcutaneous, intramuscular or intravenous routes of administration of which, intramuscular (IM) and subcutaneous (SC) injections have been the most commonly used.
Anatomically, the outer surface of the body is made up of two major tissue layers, an outer epidermis and an underlying dermis, which together constitute the skin (for review, see Physiology, Biochemistry, and Molecular Biology of the Skin, Second Edition, L. A. Goldsmith, Ed., Oxford University Press, New York, 1991). The epidermis is subdivided into five layers or strata of a total thickness of between 75 and 150 μm. Beneath the epidermis lies the dermis, which contains two layers, an outermost portion referred to at the papillary dermis and a deeper layer referred to as the reticular dermis. The papillary dermis contains vast microcirculatory blood and lymphatic plexuses. In contrast, the reticular dermis is relatively acellular and avascular and made up of dense collagenous and elastic connective tissue. Beneath the epidermis and dermis is the subcutaneous tissue, also referred to as the hypodermis, which is composed of connective tissue and fatty tissue. Muscle tissue lies beneath the subcutaneous tissue.
As noted above, both the subcutaneous tissue and muscle tissue have been commonly used as sites for administration of pharmaceutical substances. The dermis, however, has rarely been targeted as a site for administration of substances, and this may be due, at least in part, to the difficulty of precise needle placement into the intradermal space. Furthermore, even though the dermis, in particular, the papillary dermis has been known to have a high degree of vascularity, it has not heretofore been appreciated that one could take advantage of this high degree of vascularity to obtain an improved absorption profile for administered substances compared to subcutaneous administration. This is because small drug molecules are typically rapidly absorbed after administration into the subcutaneous tissue, which has been far more easily and predictably targeted than the dermis has been. On the other hand, large molecules such as proteins are typically not well absorbed through the capillary epithelium regardless of the degree of vascularity so that one would not have expected to achieve a significant absorption advantage over subcutaneous administration by the more difficult to achieve intradermal administration even for large molecules.
One approach to administration beneath the surface to the skin and into the region of the intradermal space has been routinely used in the Mantoux tuberculin test. In this procedure, a purified protein derivative is injected at a shallow angle to the skin surface using a 27 or 30 gauge needle (Flynn et al, Chest 106: 1463-5, 1994). A degree of uncertainty in placement of the injection can, however, result in some false negative test results. Moreover, the test has involved a localized injection to elicit a response at the site of injection and the Mantoux approach has not led to the use of intradermal injection for systemic administration of substances.
As taught by published US application US 2003/0050602, when a microneedle system is used for in vivo delivery, such as delivery to an intradermal space, a significant backpressure is encountered due to instillation rate of fluid volume into and essentially sealed or closed space having limited distensibility. This is true even though intradermal delivery of substances, such as medications, involve much smaller volumes if liquid, 100:L (microliters) for example, as compared with the volumes used in subcutaneous systems, which can be as large or larger than 500:L (microliters). The magnitude of backpressure is also proportional to both the instillation rate as well as the volume. This level of pressure is not typically encountered when delivering a substance to the subcutaneous or intramuscular space, which is generally regarded as a region of highly distensable tissue with a much higher limit for instilled volume.
Some groups have reported on systemic administration by what has been characterized as “intradermal” injection. In one such report, a comparison study of subcutaneous and what was described as “intradermal” injection was performed (Autret et al, Therapie 46:5-8, 1991). The pharmaceutical substance tested was calcitonin, a protein of a molecular weight of about 3600. Although it was stated that the drug was injected intradermally, the injections used a 4 mm needle pushed up to the base at an angle of 60. This would have resulted in placement of the injectate at a depth of about 3.5 mm and into the lower portion of the reticular dermis or into the subcutaneous tissue rather than into the vascularized papillary dermis. If, in fact, this group injected into the lower portion of the reticular dermis rather than into the subcutaneous tissue, it would be expected that the substance would either be slowly absorbed in the relatively less vascular reticular dermis or diffuse into the subcutaneous region to result in what would be functionally the same as subcutaneous administration and absorption. Such actual or functional subcutaneous administration would explain the reported lack of difference between subcutaneous and what was characterized as intradermal administration, in the times at which maximum plasma concentration was reached, the concentrations at each assay time and the areas under the curves.
Similarly, Bressolle et al. administered sodium ceftazidime in what was characterized as “intradermal” injection using a 4 mm needle (Bressolle et al., J. Pharm. Sci. 82:1175-1178, 1993). This would have resulted in injection to a depth of 4 mm below the skin surface to produce actual or functional subcutaneous injection, although good subcutaneous absorption would have been anticipated in this instance because sodium ceftazidime is hydrophilic and of relatively low molecular weight.
Another group reported on what was described as an intradermal drug delivery device (U.S. Pat. No. 5,997,501). Injection was indicated to be at a slow rate and the injection site was intended to be in some region below the epidermis, i.e., the interface between the epidermis and the dermis or the interior of the dermis or subcutaneous tissue. This reference, however, provided no teachings that would suggest a selective administration into the dermis nor did the reference suggest any possible pharmacokinetic advantage that might result from such selective administration.
Other methods of increasing skin permeability use various chemical permeation enhancers or electrical energy such as electroporation. Ultrasonic energy such as sonophoresis and laser treatments has been used. These methods require complex and energy intensive electronic devices that are relatively expensive. The chemical enhancers are often not suitable for intradermal drug delivery or sampling.
One example of a method for increasing the delivery of drugs through the skin is iontophoresis. Iontophoresis generally applies an external electrical field across the skin. Ionic molecules in this field are moved across the skin due to the force of the electric field. The amount and rate of drug delivery using iontophoresis can be difficult to control. Iontophoresis can also cause skin damage on prolonged exposure.
Sonic, and particularly ultrasonic energy, has also been used to increase the diffusion of drugs through the skin. The sonic energy is typically generated by passing an electrical current through a piezoelectric crystal or other suitable electromechanical device. Although numerous efforts to enhance drug delivery using sonic energy have been proposed, the results generally show a low rate of drug delivery.
Other forms of transdermal drug delivery are also known, and one such form uses pulsed laser light to ablate the stratum corneum without significant ablation or damage to the underlying epidermis. A drug is then applied to the ablated area and allowed to diffuse through the epidermis.
Another method of delivering drugs through the skin is by forming micro pores or cuts through the stratum corneum. Piercing the stratum corneum and delivering the drug to the tissue below the stratum corneum can effectively administer many drugs. The devices for piercing the stratum corneum generally include a plurality of micron-size needles or blades having a length to pierce the stratum corneum without passing completely through the epidermis. Examples of these devices are disclosed in U.S. Pat. Nos. 5,879,326 and 6,454,755 to Godshall et al.; U.S. Pat. No. 5,250,023 to Lee et al.; WO 97/48440; and WO 00/74763.
The prior methods and apparatus for the transdermal administration of drugs have exhibited limited success. Accordingly, a continuing need exists in the industry for an improved device for the intradermal administration of various drugs and other substances.
Presently, storage-stability can be imparted to medicaments by placing them in a dry powder form. Techniques for doing this include freeze-drying, spray freeze-drying, lyophilization and the like. Some dry powdered medicaments have been directly administered by inhalation. See WO 95/24183 which relates to a dry powder form of insulin for inhalation.
To date, however, there remains a need for a system for the intradermal administration of medicaments where the medicament is in a storage stable dry form, which can be readily reconstituted and directly administered via microdelivery devices such as, microabraders or microneedles and wherein the system utilizes the inherent backpressure of such intradermal or epidermal delivery to assist in the fluidic reconstitution of the dry medicament.